There are approximately 6,000 children diagnosed annually with cancer in the United States. Leukemia represents approximately 32% of all malignancies in persons less than 15 years of age. When examining children less than 1 year of age, leukemia has the second highest incidence rate and the highest mortality rate of all childhood malignancies. The annual incidence of leukemia during the first year of life is approximately 32 per million live births. We propose to investigate the role of family history and selected in utero and postnatal exposures in the etiology of acute lymphoblastic leukemia (ALL) and non-lymphoblastic leukemia (ANLL) in children 18 months of age and under. Of primary interest will be exposures resulting from medical care as well as those resulting from parental occupations and living environment. Specific exposures to be investigated included ionizing radiation, medications pesticidies, chemical solvents and petroleum products. Quantitation of risk associated with exposures and family history will be made separately for ALL and ANLL by contrasting cases to a set of age- and race-matched regional population controls (two per case). Specific medical exposures will be validated for all cases and control. In addition, assessment will be made of association between exposure and biologically defined subgroups based on malignant cell chromosomal abnormalities and cell phenotype through comparison of exposed and non-exposed cases. Analyses will be performed comparing cases of ALL to ANLL to assess possible differences in reported exposures. Lastly, reported exposures will be assessed for possible association with survival of cases.